1. Field of the Invention
The present invention relates to an ink jet printer in which maintenance processing is conducted in a state that air pressurized by an air pump is supplied to air chambers of respective ink cartridges.
2. Description of the Related Art
Various ink jet printers have been put in practical use in which color printing is generally conducted on a sheet in such a manner that a print head having a large number of ink jet nozzles that are arranged in columns jet out ink supplied from ink cartridges into ink droplets bit by bit. In those ink jet printers, a maintenance mechanism having a head cap and a cleaning blade, a suction pump, and other members are provided on a main body side thereof. To eliminate air bubbles from ink jet nozzles or to conduct a suction purge at the occurrence of nozzle clogging, the head cap is fitted to the nozzles and the ink in the nozzles is sucked by negative pressure generated by the suction pump. As a result, the air bubbles are removed or the nozzle clogging is solved.
Each ink cartridge is equipped with an ink accommodation chamber and an air chamber for exerting air pressure on the ink in the ink accommodation chamber. In printing or maintaining the ink jet nozzles, a pressure purge is performed in such a manner that pressurized air is introduced from the air pump to each air chamber via an air supply tube and ink that is pushed out of the ink accommodation chamber by the expansion of the air chamber is supplied to the corresponding nozzles.
For example, in an ink jet printer disclosed in Japanese Patent No. 2,703,647, a carriage is equipped with a color print head, a plurality of ink tanks and buffer tanks connected to the head, and other members. A pressurization pump, a waste fluid tank, a maintenance mechanism having a head cap and a cleaning blade, and other members are provided on a main body side. Air pressurized by the pressurization pump is supplied to the ink tanks via a relief valve, thereby pressurizing the ink within the buffer tanks and the ink passages of the head.
In an ink jet recording apparatus disclosed in JP-A-10-138506, a carriage is equipped with a recording head and a subtank unit. Ink cartridges that are connected to the head via supply tubes, an air pump for supplying pressurized air to the ink cartridges, a pressure regulator, a switching valve, etc., are provided on a main body side. When the residual amount of ink in a subtank becomes small, the switching valve switches so that the air pump comes to communicate with ink pouches of the ink cartridges. Air pressurized by the air pump is supplied to the ink pouches via the pressure regulator and the switching valve, and then ink is supplied from the ink pouches to the recording head and the subtank.
In conducting a suction purge, the ink within the nozzles is sucked in a state that the head cap is tightly attached to the nozzles. After completion of the suction purge, since the tightly attached head cap is removed from the nozzles in a state where negative pressure is developed in the head cap, the pressure in the head cap abruptly changes from the negative pressure to the ambient pressure. With that pressure change, the ink that has been sucked so far goes into the nozzles. In this situation, other inks that are stuck to portions around nozzles or air may go into nozzles. This raises a problem that color contamination or loss of a color may occur in the subsequent printing operation.
On the other hand, in the ink jet printer disclosed in Japanese Patent No. 2,703,647 and the ink jet recording apparatus disclosed in JP-A-10-138506, the relief valve or the pressure regulator is provided between the pressurization pump (air pump) and the ink tanks (ink cartridges). The relief valve or the pressure regulator adjusts the pressure of pressurized air that is supplied from the pressurization pump (air pump) to the ink tanks (ink cartridges). Therefore, a space for accommodating the large-size relief valve or pressure regulator is required, thereby leading to problems that the ink jet printer becomes large in size and its manufacturing costs become high.